A reflecting plate is used in a variety of fields to utilize light effectively. Presently, there is an increased interest in new miniaturized light sources such as semiconductor lasers and light emitting diodes (hereinafter, referred as LEDs).
Materials used to make reflecting plates in LEDs should have good mechanical strength and also good heat resistance with accuracy while loading on a printed wiring board (PCB). In addition, the reflecting plate is required to have a high and stable rate of reflectance (reflectivity). In particular, there is a need to minimize the rate at which reflectance (reflectivity) is reduced, which may occur due to heating during LED assembly and during the reflow soldering process. In addition, a special insert forming process can be used to make a reflecting plate with a high rate of reflectance (reflectivity), which requires a resin composition that can be used in this manufacturing process.
In this field, a material is particularly required which can withstand reflow soldering at 260° C., during which a lead-free solder is used. For that purpose, liquid crystal polymers (LCPs) or heat resistant polyamide resins have been used. LCPs can have excellent heat resistance, light resistance, and rate of flow during molding. However, LCPs can have poor adhesion with the sealing resin, such as epoxy resin, which is used during sealing with resin after installing a light emitting diode on the reflecting plate. Moreover, the LCP may not provide sufficiently high reflectance (reflectivity) as a reflecting plate, because the whiteness of the resin is low.
Aliphatic polyamides (such as PA6, PA66, PA11, and PA12) can have excellent strength and injection molding formability. Such polyamides, however, do not have heat resistance sufficient to withstand high temperatures during the reflow soldering process. In addition, these polyamides can have a low rate of absorption and thus the reflectance (reflectivity) can be reduced since its color changes during heating.
International Publication No. WO 2003-085029 and Japanese Patent No. 1995-228776 are directed to a polyamide resin for a reflecting plate of a light emitting diode. The composition is made by mixing inorganic fillers with polyamide resin comprising 1,9-diaminononane as a diamine. However, in these polyamide resins may not sufficiently prevent decreased reflectivity resulting from heat in the LED assembly and reflow soldering process. Also the composition may not exhibit good adhesive property with the sealing resin.
Japanese Patent No. 2002-294070 is directed to a polyamide resin to which potassium titanate fiber and/or wollastonite are added. However, the polyamide resin composition may not exhibit sufficient strength during a molding process and thus there can be problems using the same in insert molding.
Japanese Patent No. 2001-115015 is directed to a polyamide resin which can reduce discoloration in the molded product by using a specific photostabilizer. However, in this method, since some portion of the resin is attached to the mold during the molding process, the productivity can be affected.